Blow lance arrangement

ABSTRACT

A blow lance arrangement for controlling flow of gas through a blow lance arranged to blow gas onto the upper surface of a metal bath by moving the end of a spindle arranged in a longitudinal passage of the blow lance from a retracted position located upwardly spaced from a restricted throat portion of the passage through the throat portion to advanced positions into the outwardly flaring nozzle portion of the passage.

United States Patent [72] Inventors JyoDoi Kanagawa-ken;

Kunio Yoshioka, Kanagawa-ken, both of Japan [2]] App]. No. 32,997

[22] Filed Apr. 29, 1970 [45] Patented Dec. 14, 1971 [73] AssigneeNippon Kokan Kabushiki Kaisha Tokyo, Japan [32] Priority July 27, 1966[33] Japan Original application July 26, 1967, Ser. No. 656,241, nowabandoned. Divided and this application Apr. 29, 1970, Ser. No. 32,997

[54] BLOW LANCE ARRANGEMENT 6 Claims, 12 Drawing Figs.

[52] U.S. Cl 266/34 L,

75/59 [51] Int. Cl C2lc 7/00 [50] Field of Search 266/34,

DIG. 3, DIG 4; 75/59, 60

[56] References Cited UNITED STATES PATENTS 3,346,190 l0/l967 Shepherd75/60 X FOREIGN PATENTS 216,032 7/196] Austria i. 266/34 224,669 l2/l962Austria.... 266/34 995,688 6/1965 Great Britain.v 266/34 l,()()3,5 l49/[965 Great Britain 266/34 Primary l-jxamim'n-Gerald A. DostAlmrnvy-Michacl S. Striker ABSTRACT: A blow lancc arrangement forcontrolling How of gas through a blow lance arranged to blow gas ontothe upper surface of a metal bath by moving the end of a spindlearranged in a longitudinal passage of the blow lance from a retractedposition located upwardly spaced from a restricted throat portion of thepassage through the throat portion to ad vanced positions into theoutwardly flaring nozzle portion of the passage.

PATENIED BEE I 4 mm ISOOO- IZ-OOO lOOOO IO-O SHEET 3 OF 6 Tl Ifi 6 Pr Q"Van ab;

Pr 7 /cm abs In) #901" k who ymmm 4 BLOW LANCE ARRANGEMENTCROSS-REFERENCE TO RELATED APPLICATION The present application is adivision of our copending patent application Ser. No. 656,241, filedJuly 26, 1967, entitled Method of Making steel," and now abandoned.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a blowlance arrangement.

As well known the converter operation may comprise inserting a watercooled lance through the opening in an upright furnace, blastingindustrially pure oxygen onto the surface of steel bath containing hotmetal as main raw material from a height in the order of l-2 m. to forma fire spot, thereby effecting a quick oxidizing reaction. In such anoperation, i.e. in a refining process for obtaining steel havingrequired chemical analysis values from hot metal with addition of somescrap, the proper oxidation of above charged raw materials iscomplicated. It has been a long-pending question in industrial circleshow to properly control flow rate and pressure of the oxygen used. Inthe LD process, especially in the last blowing stage, as a consequenceof the decrease of decarburizing reaction, it is well known that theboiling drops. In order to cope with the phenomenon of rapid increase of[N], which is caused by the air drawn into the furnace owing toconsiderable reduction of internal pressure of the furnace, the oxygenjet pressure should be increased. However when the pressure of oxygensupplied is raised, the flow rate of oxygen is also increased. Thisproduces a bad effect, namely the increase of oxygen content in thesteel. Nevertheless, under present circumstances where no appropriatemeasure for solving this problem exists, a step such as increase of thepressure of the oxygen supplied, neglecting said undesirable effect ofblowing at a lowered lance height above bath is taken. In this case themethod of controlling flow rate and pressure of oxygen with a loweredheight has naturally a limit, because the possibility of deformation andburning of the nozzle increases and the area of the oxygen jet whichcomes into contact with the steel bath is considerably reduced.

Moreover with increase of furnace capacity, the use of plu ral lanceshas been proposed, because a single lance provides limited reaction.However, this method is impracticable due to difficulties in an actualequipment. As a substitute for this method, a multinozzle, that is, anozzle provided with three or four holes to jet oxygen has beensuggested. However similarly to a usual single hole nozzle, it is unableto perform an operation, in which only increase of oxygen pressure isobtained without increasing its blow rate, or vice versa, incorrespondence to the oxidizing reaction. The present invention aims toovercome the shortcomings of nozzles (including nozzle system) hithertoproposed and used, and to solve their com mon shortcomings.

According to the present invention, firstly, one and the same lancepermits to select an optional flow rate or pressure of oxygen as desiredaccording to respective steps of blowing and it is possible to eliminatethe necessity of changing the lance height above the bath or the oxygenflow rate and to permit, under the same conditions of oxygen supply, tochange the flow rate or pressure of the jet hitting upon the surface ofthe bath and in some cases also the shape and area of the fire spot, asdesired, secondly, when applied to a large-sized converter in which thebath tends to be shallow, the lance also permits to use the furnace toits maximum efficiency, and thirdly, irrespective of the capacity of thefurnace, the efficiency and yield can be improved and at the same timesuch a phenomenon as superoxidation of the bath can be prevented, so asto reduce oxygen, nitrogen and other impurities in the steel, so that agood quality steel can be obtained.

Now to consider oxygen flow rate and pressure in connection with asectional area of lance, there seems to be a relation:

wherein V: Flow rate of oxygen NmP/min.

P: Oxygen pressure kg./cm.

K: Constant 1.04 Nmfilkg. min., 300 K.

a: Sectional area cm. (constant) It can be seen that if the flow ratechanges, the pressure also changes proportionally and vice versa,because the sectional area at a point of the lance does not change butremains constant. The inventors of the present application discovered intheir examination that the blowing function in the use of oxygen can beeasily and basically varied by adjusting the sec tional area of thethroat portion of the lance nozzle. The known characteristics of thesupersonic oxygen jet has a function that, different from staticoxidation reaction in open hearth furnace, its impact pressure forms adepression on the bath surface and then accelerates agitation andcirculation of the bath, thereby oxidizing the bath directly. It is wellknow that for obtaining such an impact pressure, the sectional area ofthe nozzle throat has a great effect and is determined in connectionwith the expansion ratio of the cross section of the nozzle outlet.Briefly it may be said that a jet velocity is obtained by the drivingpressure elevated by throttling the passage of oxygen, followed byjetting said oxygen at an appropriate inclination angle. This is why theinventors selected the nozzle throat as point for controlling flow rateand pressure of the oxygen jet during the blowing performance.

Now, if the flow rate of oxygen is constant, it is possible by changingthe sectional area of the throat to obtain an oxygen pressurecorresponding to this change. The converse is also possible. Aneffective and appropriate flow rate or pressure must be held inaccordance with respective steps in the blowing operation. An attempt tocontrol the sectional area of the throat merely by inserting a spindleof appropriate diameter into the throat of a single-hole nozzle left inplace showed a very good result.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a partially broken front viewof an embodiment of the present invention;

FIG. 2 is a sectional view of the lower portion of lance of the same;

FIG. 3 is a sectional view along A-A of FIG. 2;

FIGS. 4 and 5 show respectively embodiments of nozzle mechanism;

FIGS. 6 and 7 show graphs of flow rate of oxygen and its pressureaccording to change of the sectional area of the throat portion of thenozzle mechanism of FIG. 41;

FIGS. 8 and 9 show graphs of oxygen and nitrogen content as used effectsof FIG. 4 nozzle applied to practical operation;

FIG. shows in a graph the relation between jet inclination angle innoule mechanism of FIG. 5 and gross yields;

FIG. Ill similarly shows an example of the relation between and point[C] and slag T.Fe; and

FIG. 12 is an explanatory view of the tire spot on the bath surfaceduring the use of the nozzle shown in FIG. 5.

An explanation will be given as follows with reference to an embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a lance hangermechanism 1 is identical with a prior art mechanism, and on both sidesthereof are formed a supporter I". In an intermediate portion of thesupporter I", other supporters I are formed near the joint portion oflance pipe 8. A selysin transmitter 2 provided in the upper portion ofthe lance L senses the position of the spindle I3 inserted into thelance and said position is transmitted, for instance, to a furnaceoperation room in the form of electric signals for indication. Thefurnace operator can know the position of spindle 13 in the lance bythis indication and then operate a small motor 3 to fix spindle 13 inthe position corresponding to the reaction in the furnace through themedium of a gear mechanism. In this case, in order to limit up and downmovement of the spindle 13, a limit switch is preferably attached.Handle 4 serves for manual driving of spindle 13. A stufiing box at theportion of the oxygen supply pipe which is pierced by spindle 13prevents leakage of oxygen gas at this location. The lance body istightly connected with the oxygen supply pipe 8 by a coupling, and inletpipe 9 and outlet pipe 10 for cooling water communicating with passages17, 18 concentrically outside around oxygen flow-in tubular passage 16are likewise connected to the valve body. The gland 20 serves forsealing the joint portion of oxygen flow-in pipe 16 and inlet pipe 9.Support members 11 and 12 are provided for supporting oxygen supply pipe8, cooling water inlet pipe 9 and outlet pipe 10.

Into oxygen flow-in pipe 16 of the lance of above construction, spindle13 is inserted movably up and down as aforementioned for such a distancethat the head of spindle 13 reaches approximately the head of the lancenozzle in the lower limit of movement of the spindle. Such structure isof importance for obtaining the optimum jet conditions in the presentinvention. Spindle 13 which is eminently efiective by itself may provemore effective, if appropriately tapered in the head member 14. The headmember 14 may be changed during a blowing operation and spindle 13 isconnectable with a head member by screw mechanism 21 for simple andquick change of said head member and easy mounting and dismounting ofhead members of various shapes. Further for preventing vibration of thespindle, which causes irregular change of sectional area of the nozzlethroat during a blowing operation, a spindle holder 15 is fixed tospindle 13 and engaging the inner surface of oxygen flow-in passage 16.

Generally, there is a limit in the impact pressure applied on the bathby the oxygen jet during blowing. The sectional area of nozzle throat TTshown in FIGS. 4 and 5 is designed in relation to the flaring of thenozzle outlet opening E-E shown in FIG. 4 in such a manner that nosplash from the depression thereof is formed by the jet impact pressure.Such sectional area of throat can be changed by the depth of insertionof the spindle head. The diameter of spindle throat B-B should bedetermined carefully so that the driving pressure I reaches the maximumpressure required at the nozzle exit C-C. Such driving pressure I andnominal impact pressure in the singlehole nozzle can be changed bymovement of spindle 13 so as to cope with any reaction in furnace, andeasily controlled in small steps.

These proportional relative dimensions vary in accordance with changesof capacity and shape of the furnace. If the head of the spindle isappropriately tapered from the portion facing the nozzle throat so as tochange sectional areas of said head progressively, more effectivenesswill be obtained.

FIG. 6 shows the flow rate of oxygen in accordance with variation of thenozzle sectional area TT by changing the position of the spindle head ofFIG. 4, on the supposition that oxygen supply pressure is constant. FIG.7 shows the driving pressure I in accordance with variation of thethroat sectional area on the supposition that oxygen flow rate isconstant. In this example, blowing is carried out at the oxygen flowrate of 12x10 NmF/hr. and the pressure of 8 kg./cm. with the spindlehead pulled up to the position shown in dotted line in the uppermostpart of FIG. 4. In the last stage of blowing performance, the nozzlehead tip point is lowered to the end of the lance and blowing iscontinued with said spindle head in the position 14b. The distance ofthe lance was kept constantly 1,350 mm. from the upper surface of themetal bath.

As condition of blowing at that time, the oxygen driving pressure P, wasincreased approximately to l5 l g./cm. abs, while the flow rate of theoxygen was maintained. FIG. 8 shows in a graph results of experimentsestablishing the oxygen constant of a melt relatively to the carboncontent at the end of operations made by adjusting relation between saidpressure and flow rate by above-mentioned lance conditions. FIG. 9consolidates numerous results of experiments on [N] relatively to [C] atthe end of similar operations. In FIG. 8, the percentages of [C] and [O]at the end of the blowing operation are lower in the operation using thelance of the present invention than in operation using an ordinarylance. In FIG. 9 to all values of C at the end of the blowing operationthe percentage of [N] to [C] is lower when a lance of the presentinvention is used. Especially when an ordinary lance is used, [N]increases linearly from a position at about 0.07 percent of end point[C], whereas when the lance of the present invention is used, [N]decreases progressively with decrease of end point [C] so that in steelhaving low end point [C] undesirable effect of [N] can be markedlyimproved.

Such advantage can be attributed to the fact that the rate of flow ofoxygen and its pressure for blowing can be easily selected as desired bythe present invention. Namely in the last stage of the blowingoperation, the agitation of the bath weakens with advancement ofdecarburization and the furnace pressure markedly drops with thetendency of becoming lower than atmospheric pressure so that the airdrawn into the furnace abruptly increases [N]. Accordingly, in order tocope with such a phenomenon, oxygen supply pressure is commonly raised.However in ordinary lances, the increase of oxygen supply pressurecannot avoid the increase of the flow rate, resulting in an unnecessarysuperoxidation of the bath and the slag, to cause increase of said [0].However the use of a lance of the present invention enables to controlflow rate or pressure of oxygen as desired. Thus the increase of oxygenpressure, as a countermeasure to the drop of furnace pressure in thelast stage' of blowing performance, does not cause an increase of theoxygen flow rate so that the phenomenon of superoxidation of the bathcan be avoided. It is apparent from above explanation that the more theend point of [O] is lowered, the greater will be the beneficial effectsof a lance of the present invention. Further,'the controlling of theoxygen flow rate or its pressure during blowing as desired caneffectively eliminate [P], [S] [N] and other impurities in the steel.

To sum up effects and merits obtained by experimental operations, whenthe oxygen flow rate is changed while the oxygen pressure is keptconstant, the velocity of decarburization can be changed without changeof [0] in the steel and T, Fe in the slag, and at the same time such aslopping which is generally apt to occur can be completely prevented.

Conversely, when the oxygen pressure is changed, while the oxygen flowrate is kept constant, [0] and [P] in the steel and T, Fe in the slagcan easily be controlled without changing the velocity ofdecarburization, which is not obtainable with lance constructionsaccording to the prior art.

The shape of the passage through the nozzle head is also of importanceand preferably the cross section of the passage gradually increases fromthe throat TT toward the bottom end, as shown in FIG. 5. This canbasically change the fire spot made by an ordinary nozzle so as to copewith increase of surface area of the bath.

The essential feature of said nozzle passage resides in the degree oftaper as aforementioned. Although a taper must of course be decided inrelation to the degree of an ordinary nozzle taper, it can be said thatthe taper should be constructed in such a manner as to demonstrate itsmaximum efficiency when it is used in a normal single-hole nozzle.

Now when the spindle head 14c in FIG. 5 is lowermost positioned, theimpact area on the bath surface increases and looks like a ring, asshown in FIG. 12b. Such ring-shaped fire spot, concentric with thefurnace wall becomes well capable of coping with an increase of the bathsurface area. This nozzle construction can be said to be ideal for afurnace near the end of life or in which the bath has been shallowed byincrease of furnace capacity. In the here exemplified operation, keepingthe oxygen flow rate constant, the driving pressure with the head 14cpositioned at the lowermost limit, as shown in TABLE Position of SpindleUppermost Limit Lowermost Limit The table shows that the agitation andcirculation of the bath were active with eminent results as shown inFIGS. 10 and 111. FIG. 10 compares the tapping yield obtained byprogressively changing the degree of taper in FIG. with that obtained bysingle-hole nozzle lance used in the same furnace. This shows that theoperation using a nozzle construction of the present invention resultsin a higher tapping yield than a single-hole nozzle irrespectively ofdegree of the spindle head taper, and, when jet inclination angle 6 isnot less than 6, the tapping yield by using our nozzle is superior tothat of three-hole nozzle. FIG. 11 shows the percentage of T, Fe in theslag in relation to the final percentage of carbon, compared with thoseobtainable when a three-hole nozzle was used. it can be said that thiscannot too much demonstrate the usefulness of nozzle mechanism of thepresent invention. These goods results are attributed to the fact that,as shown in H0. 12, the jet obtained by the present invention forms aringshaped fire spot concentrally with the furnace wall and thatagitation and circulation of the bath produced by said fire spot couldwell cope with an increased surface area ofthe bath. It is needless torepeat that such bath conditions also showed an eminent result inremoving impurities from the steel such as [P] and [S], to say nothingof [O] and [N]. Although, in above-mentioned method, we increased theoxygen pressure while maintaining a constant oxygen flow rate, therelation between flow rate and pressure of oxygen may be changed freelyin accordance with the shape of the furnace and blowing condition for anappropriate operation as mentioned in connection with nozzle mechanismshown in FIG. 4.

As above mentioned, the lance for steel making according to the presentinvention enables to make an effective and appropriate blow of oxygenonto a metal bath which completes blowing in a short time and can wellcope with a shallow bath being caused by using the furnace at shortintervals and increasing the capacity of the furnace, thereby bringingabout a high yield and quality. Moreover the lance of the presentinvention is of rigid and simplified construction and can be very easilyoperated. Said lance can be made by a simple modification of an ordinarysingle-hole lance.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention,and therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended l. A blow lance arrangement for blowing gas ona metal bath, said arrangement comprising, in combination, supportmeans; an elongated blow lance supported on one of the ends thereof onsaid support means with the other end thereof adapted to be locatedadjacent to a metal bath, said blow lance being formed with an axialpassage therethrough having adjacent to said other end a throat portionof a predetermined length and of an open cross section smaller than theremainder of said passage and downstream of said throat portion anoutwardly flaring passage portion of a greater length than that of saidthroat portion and extending between the latter and said other end ofsaid blow lance; means for feeding gas under pressure in the region ofsaid one end of said blow lance into said axial passage thereof; andmeans for changing the open cross section of said throat portion andthat of said outwardly flaring passage portion and comprising spindlemeans arranged in said passage and comprising a cylindrical rod and atapering head on one end of said rod, said tapering head having amaximum diameter smaller than the diameter of said throat portion and alength substantially equal to that of said flaring passage portion, andmeans connected to the other end of said rod for moving said spindlemeans in longitudinal direction of said passage between a retractedposition in which the free end of said tapering head is located betweensaid one end of said blow lance and said throat portion and an advancedposition in which said free end is adjacent to said other end of saidblow lance.

2. An arrangement as defined in claim 1, wherein said spindle meanscomprises a cylindrical rod, a pair of tapering spindle heads, andcooperating attaching means on corresponding ends of said rod and saidspindle heads for selectively attaching said heads to said rod, each ofsaid heads having at the attaching end a cross section equal to that ofsaid rod and one of said heads tapering from the region of saidattaching end towards the free end thereof and the other of said headsflaring outwardly toward said free end to a cross section smaller thanthat of said throat portion.

3. An arrangement as defined in claim 1, and including indicating meanscooperating with said spindle means for indicating the position of thelatter relative to said blow lance.

4. An arrangement as defined in claim 1, wherein said spindle head isremovably attached at one end thereof to said one end of said rod, andwherein said one end of said spindle head has a diameter equal to thatof said one end of said rod and tapers from said one end of said headtoward the free end thereof.

5. An arrangement as defined in claim 11, wherein said spin dle head isremovably attached at one end thereof to said one end of said rod, andwherein said one end of said spindle head has a diameter equal to thatof said one end of said rod, and wherein said spindle head flares fromsaid one end thereof outwardly to its free end.

6. An arrangement as defined in claim 5, wherein said cone angle of saidoutwardly flaring spindle head is substantially equal to the cone angleof said outwardly flaring passage portion of said nozzle.

1. A blow lance arrangement for blowing gas on a metal bath, saidarrangement comprising, in combination, support means; an elongated blowlance supported on one of the ends thereof on said support means withthe other end thereof adapted to be located adjacent to a metal bath,said blow lance being formed with an axial passage therethrough havingadjacent to said other end a throat portion of a predetermined lengthand of an open cross section smaller than the remainder of said passageand downstream of said throat portion an outwardly flaring passageportion of a greater length than that of said throat portion andextending between the latter and said other end of said blow lance;means for feeding gas under pressure in the region of said one end ofsaid blow lance into said axial passage thereof; and means for changingthe open cross section of said throat portion and that of said outwardlyflaring passage portions and comprising spindle means arranged in saidpassage and comprising a cylindrical rod and a tapering head on one endof said rod, said tapering head having a maximum diameter smaller thanthe diameter of said throat portion and a length substantially equal tothat of said flaring passage portion, and means connected to the otherend of said rod for moving said spindle means in longitudinal directionof said passage between a retracted position in which the free end ofsaid tapering head is located between said one end of said blow lanceand said throat portion and an advanced position in which said free endis adjacent to said other end of said blow lance.
 2. An arrangement asdefined in claim 1, wherein said spindle means comprises a cylindricalrod, a pair of tapering spindle heads, and cooperating attaching meanson corresponding ends of said rod and said spindle heads for selectivelyattaching said heads to said rod, each of said heads having at theattaching end a cross section equal to that of said rod and one of saidheads taperIng from the region of said attaching end towards the freeend thereof and the other of said heads flaring outwardly toward saidfree end to a cross section smaller than that of said throat portion. 3.An arrangement as defined in claim 1, and including indicating meanscooperating with said spindle means for indicating the position of thelatter relative to said blow lance.
 4. An arrangement as defined inclaim 1, wherein said spindle head is removably attached at one endthereof to said one end of said rod, and wherein said one end of saidspindle head has a diameter equal to that of said one end of said rodand tapers from said one end of said head toward the free end thereof.5. An arrangement as defined in claim 1, wherein said spindle head isremovably attached at one end thereof to said one end of said rod, andwherein said one end of said spindle head has a diameter equal to thatof said one end of said rod, and wherein said spindle head flares fromsaid one end thereof outwardly to its free end.
 6. An arrangement asdefined in claim 5, wherein said cone angle of said outwardly flaringspindle head is substantially equal to the cone angle of said outwardlyflaring passage portion of said nozzle.